rcS: Fix the annoying "init: starting pid XYZ, tty '/dev/hvc0': '/bin/sh, not found"

rcS: Fix the annoying "init: starting pid XYZ, tty '/dev/hvc0': '/bin/sh, not found"

The reason the /etc/inittab was not re-read (even
thought we did an kill -1 1 within this startup
script) is b/c:

(from busybox/init/init.c)
/*
 * NB: while SYSINIT/WAIT/ONCE are being processed,
 * SIGHUP ("reread /etc/inittab") will be ignored.
 * Rationale: it would be ambiguous whether SYSINIT/WAIT/ONCE
 * need to be rerun or not.
 */

and init.d/rcS is SYSINIT - so no SIGHUP can be done as
that is running. As such we just spawn a nohup subprocess that will
do it for us.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>